Research carried out by Professor Leon Feinstein suggests that social class factors begin to have a major impact on intellectual development even before children enter nursery school. Higher social class children who score well on a range of tests at twenty two months tend to maintain their initial relatively high rankings while higher social class children who initially score badly tend to improve. Meanwhile initially high scoring lower social class children tend to slip back and progress for initially low scoring lower class children is slow. Professor Feinstein also shows that children's performance in tests at age 22 months is a strong predictor of their subsequent chances of gaining A level passes. [ Life Chances and Social Mobility: An Overview of the Evidence: Stephen Aldridge 2004  for the  Cabinet Office]